Why, for instance, would they have resorted to cannibalism? What harsh conditions caused the wear and tear evident on surviving bones?

There are two possible reasons why Neanderthals would have dined on their dead, according to lead author Dr Antonio Rosas, a scientist in the palaeobiology department at the National Museum of Natural Sciences in Madrid.

"One is that they needed to eat whatever was at hand, including human flesh, because ecological conditions for their survivorship, such as extreme cold weather and no meat from hunting, were really hard," Rosas says.

The other possibility, he says, is that "this was done in the context of something we may think of as symbolic".

Rosas suggests the virtual absence of animal remains at the site, a cave called El Sidrón, may point either to ritual killings or unsuccessful hunting. Neanderthals are thought to have subsisted primarily on meat.

Toothy clues

The Neanderthals studied ranged in age from infancy to young adulthood. Their teeth revealed that tooth growth often stopped abruptly due to illness or malnutrition.

Adolescence in general appears to have been a particularly hard time, possibly due to separation from parents and the resulting need for self-sufficiency.

Cut marks associated with butchery were found on some of the remains, particularly those of the younger individuals.

The skeletal remains also reveal that these Neanderthals possess a different bone structure than individuals found elsewhere in Europe.

It appears that Neanderthals fell into at least two basic ethnic groups that coincided with their north-south geographical distribution.

Southern Neanderthals from the Iberian Peninsula, the Balkans, the Middle East and Italy had broader and shorter faces than northern Neanderthals from populations living north of the Pyrenees, the Alps, portions of Asia and central and eastern Europe, the researchers say.

Scientists are now debating whether interbreeding with modern humans occurred and why all of these Neanderthal groups appear to have gone extinct.

"It does look, from a variety of data, that Neanderthals were subject to episodes of extreme scarcity, with which their cultural and social systems sometimes couldn't cope," says Professor Steven Kuhn, an anthropologist at the University of Arizona.

"There could also be a link between boom-and-bust subsistence and occasional cannibalism."

Sharing out the chores

Kuhn and colleague Professor Mary Stiner theorise that modern humans better divided labour along the lines of gender and age.

Instead of everyone working toward the next big kill, women and children in early modern human groups devised other food-obtaining strategies, such as gathering fruits and nuts.

"That's what allows people to negotiate and maintain their complex patterns of dependency and cooperation, keep each other in line, etc. But whether the cognitive development is cause or consequence isn't clear to us."